1. Field of the Invention
The present invention relates to a fingerprint input apparatus for optically reading a fingerprint, and more particularly to a fingerprint input apparatus having an input section, which is smaller in area than a finger to be an input object, and requiring a plurality of input times while moving the finger in order to obtain a fingerprint image of the entire finger.
2. Related Background Art
Conventionally, a fingerprint has been used as important information to identify an individual person. In recent years, however, a fingerprint is optically input and electronically processed as image information.
A fingerprint input section in a fingerprint verification/authentication device for use in this type of processing is preferably as compact as possible for mounting. If the fingerprint input section, however, is smaller in area than the finger, fingerprint information of the entire finger cannot be obtained at a time. Therefore, if a fingerprint input section smaller than the finger, it is necessary to enter partial fingerprint information acquired from different parts of the finger a plurality of number of times by moving the finger on the input section, to calculate relative locations of the partial fingerprint information by an arithmetic operation, and to reconstruct the entire fingerprint information from the partial fingerprint information.
Referring to FIG. 5, there is shown a block diagram of a configuration of the conventional fingerprint input apparatus requiring an acquisition of these partial fingerprint images.
The conventional fingerprint input apparatus 1 shown in FIG. 5 comprises: a fingerprint input section 11 for acquiring partial fingerprint images from a finger; a storing section 12 having a storage area 121 for storing the acquired partial fingerprint images; a communication section 14 connected to an external device 6; and a control section 15 for controlling operations of these sections 11, 12, and 14. With this configuration, the fingerprint input section 11 acquires the partial fingerprint images of the finger and stores them into the storing section 12, so that the partial fingerprint images are output from the storing section 12 to the external device 6 via the communication section 14, under the control of the control section 15.
The fingerprint input apparatus 1 does not include an operation section. The storing section 12 is only used as a temporary storage location for the partial fingerprint images (In some other cases, the fingerprint input device 1 does not include the storing section 12 like the operation section, either). Therefore, signals output from the fingerprint input apparatus 1 are only of the partial fingerprint images.
The external device 6, which is connected to the fingerprint input apparatus 1 and disposed separately from the fingerprint input apparatus 1, performs the arithmetic operation for reconstructing the entire fingerprint information from the partial fingerprint information output from the fingerprint input apparatus 1 in this manner. The external device 6 specifically performs the operation of calculating a relative location between a certain partial fingerprint image and other partial fingerprint images, in other words, a distance, a direction, or an angle of rotation of the finger movement between the current partial fingerprint image and the past partial fingerprint images. To calculate the relative location between both partial fingerprint images by this operation, the partial fingerprint images need to include information acquired from the same position of the finger.
On the other hand, the fingerprint input section 11 is required to be as compact as possible. This causes an area of the partial fingerprint images that can be acquired at a time to be inevitably small. In this case, the time intervals for acquiring the partial fingerprint images need be considerably short in order to calculate the relative location so as to correspond to an actual finger movement speed.
Referring to FIG. 6, there is shown a diagram illustrating a relation between the finger and the finger input section. For example, if the vertical length of the fingerprint input section 11 is H mm shown in FIG. 6 and the movement speed of the finger 5 is V mm/sec in the direction indicated by an arrow, an upper limit T sec of the time intervals for acquiring images necessary for the partial fingerprint images sequentially acquired to include information from an identical part of the finger can be calculated by T=H/V. The length H of the fingerprint input section 11 that is practically small enough is considered about 0.5 mm. Moreover, the fingerprint input section 11 cannot be considered practical unless it can cope with the finger movement speed v of 200 to 300 mm/sec. The upper limit T of the time intervals for acquiring the images in this case is within a range of 2.5 to 1.7 ms (T=2.5 to 1.7 [ms]) on the basis of the above equation.
If a sequential operation is performed whenever a partial fingerprint image is acquired, it is necessary to communicate the fingerprint image and to calculate the distance during the time T. It requires a great deal of computing power. This inhibits the external device 6 to perform any other processing during the input of the fingerprint. Therefore, processing of converting the fingerprint images to information for verification and authentication or processing of performing the verification and authentication is started only after the input of the fingerprint completely ends. Thereby, a user needs to await the end of the processing to obtain a result of the verification and authentication, which makes the apparatus unavailable.
Alternatively, there can be a processing method in which only image acquisition is performed during the fingerprint input and the distance calculations are done collectively after the end of the input. This method, however, makes no difference in that the information conversion, verification and authentication can be performed only after the end of the fingerprint input, and a user is still kept waiting until the end of the processing. Furthermore, this method requires a large storage area for storing all of the acquired partial fingerprint images. The reservation of the storage area has a problem of causing an increase in size of the external device or an increase in power consumption.
Moreover, naturally the external device 6 requires software for an image comparison operation or a distance calculation. Therefore, it has caused problems of complicating the software and requiring an area for storing the software and the time for performing the image comparison operation collectively after acquiring all images.
As known examples for resolving these problems, there are means suggested in JP-A-2001-184490 and JP-A-H10 (1998)-255050. These means measure a moving direction and distance of a finger movement by providing a detecting device, which is different from that for image acquisition, such as a roller for causing the finger to contact with an input section or a slider with a finger holder fixed.
The means disclosed in the JP-A-2001-184490 and JP-A-H10(1998)-255050, however, cause an increase in size of the fingerprint input apparatus due to the additional detecting device undesirably. Furthermore, these means each have a movable part, which presents a problem of causing concern about a breakdown or a trouble and therefore inhibiting an increase in reliability of the apparatus.